Dual-Fuel LNG Tractor Tug Delivered to Turkish Owner

The 39-metre tug Silivri has been delivered to The BOTAS Petroleum Pipeline Corporation in Turkey.

The TRAktor V3900-DF series tug was recently completed at Uzmar Shipyard to a design by Robert Allan Ltd.

Silivri is only the second vessel in the world to combine Voith Schneider propulsion with dual-fuel LNG/diesel engines. This unique arrangement has only been combined once before, on her sistership Sultanhani, delivered earlier in the year to the same owner.

Equipped with Wärtsilä 6L34DF engines and 32X6 Voith Schneider propellers, Silivri can undertake challenging escort operations as part of Botas’ fleet. VSPs are well suited for this application due to their fast response time and precise maneuvering. The 32X6 VSP model is the latest innovation in cycloidal propeller design, featuring several improvements over its predecessors, not least of which is a simplified yet more robust design.

The TRAktor V3900-DF series also features a new geometry for the VSP guard plate, optimizing bollard pull performance and simplifying construction.

The Wärtsilä 6L34DF dual fuel engine can run on either natural gas or diesel, with seamless transition between the two fuels. An exhaust aftertreatment arrangement consisting of SCR units, mixing tubes, and a dedicated diesel exhaust fluid (DEF) system are installed on the vessel to maintain IMO Tier III emission compliance even in diesel operating mode.

The 40m3 LNG tank is fitted aft of the engine room in a dedicated compartment and is installed transversely allowing a more compact and efficient equipment arrangement, as well as separating associated hazardous zones from the accommodation block forward. A force ventilated LNG vent mast allows possible vented natural gas from the LNG tank and system to be well dispersed on exit, without the potential for cold vapor collapse. The vent mast locates the outlet well above the working deck and away from any crew areas or ventilation intakes.

Silivri’s wheelhouse design enables 360-degree visibility for the master and features two control stations (one forward, one aft), each with full functionality. Critical deck equipment like the heavy-duty escort winch and dedicated staple are fully visible from the aft control station. From this same location both fire-fighting monitors are visible in their position on an aft elevated platform.

Development of the TRAktor V3900-DF hull form included an extensive computational fluid dynamics (CFD) phase in which multiple operational parameters were optimized. Foremost among those was ensuring excellent tug directional stability by installing Robert Allan Ltd.’s strake stabilizers at the stern of the tug. These small appendages ensure the tug is directionally stable yet still highly maneuverable, with very minimal impact to resistance. During the design phase these results were verified in model tests and results were confirmed on sea trials.

Silivri can generate 80 tonnes of bollard pull and 107 tonnes of steering force during escort operations. The Silivri can also achieve 188 tonnes of braking (more than two times the static bollard pull).

This tug represents the latest evolution of the design concept developed by Robert Allan Ltd. for LNG-fueled tugs. It addresses the space and regulatory limitations specific to small vessels, which are not present in larger LNG-fueled vessels. This design incorporates lessons learned and operational feedback from the 10 previous Robert Allan Ltd. designed LNG-fueled tugs. Many of these design features are now being used as the foundation for future alternatively fueled tug designs under development at Robert Allan Ltd.

The tug was designed and constructed to comply with all applicable Rules and Regulations of Bureau Veritas.

Particulars of the TRAktor V3900-DF series are:
Length overall: 39.0m
Beam, moulded: 15.0m
Depth, moulded: 6.0m
Gross tonnage: 900

Tank capacities are as follows:
Diesel Fuel oil: 164m3
LNG: 40m3
Potable water: 23m3

Sea trial results showed that the Silivri achieved and surpassed all requirements:
Bollard pull, ahead: ~80 tonnes
Free running speed, ahead: ~12.5 knots